Arcuate path electron beam tube for past
wave signal amplification



June 28, 1966 H. HART 3,258,702 ARCUATE PATH ELECTRON BEAM TUBE FOR FAST WAVE SIGNAL AMPLIFICATION Filed Sept. 19, 1961 & 25 Z4 -3' acisu fiu 50mm; PMF' Z6 6 7 45 4? HWY 42 INVENTOR PAUL A. H. HART United States Patent 6 Claims. in. sac-4.7

The invention relates to a device comprising an electron beam tube for signal amplification with the aid of a fast wave, the tube comprising at least three coupling members arranged in order of succession between the electron gun and a collector electrode, in the direction of travel of the electrons, the signal to be amplified being supplied to the first coupling member, which produces an electric field acting transversely on the beam, so that a fast wave is obtained, a pumping signal being fed to a second coupling member, which produces an inhomogeneous, electric field acting transversely on the beam, whilst through the fast wave the amplified signal is obtained from the third coupling member. The invention furthermore relates to an electron beam tube for use in such a device.

With such devices it is known to focus the electron beam usually by means of a substantially homogeneous magnetic field, of which the lines of force extend parallel to the electron beam. Under the action of the axial magnetic field and of the transverse electric field produced by the first coupler, the beam electrons assume a helical movement having an orbital frequency which is termed the cyclotron frequency f,,. The frequency of the pumping signal fed to the second coupler is then equal to twice the cyclotron frequency f If the signal frequency f, is not equal to the cyclotron frequency it is found that the signal propagation may be described by two transverse waves, which are termed the fast wave and the slow wave.

The shape and the dimensions of the first coupler may be chosen so that at least theoretically only the fast Wave is produced.

The shape, the dimensions and the load of the third coupler are chosen so that this coupler is coupled with the transverse fast wave and absorbs, in principle, all signal energy coming in.

The amplification is obtained at the expense of the energy supplied by the pumping signal source in the form of an inhomogeneous electric field acting mainly transversely upon the beam, the frequency thereof being equal to twice the cyclotron frequency. Prior to the electrons entering this second coupler, the radius of the helical path of the electrons is proportional to the amplitude of the signal to be amplified. If the forces acting upon the electrons within the second coupler are proportional to the radius of the path of the electron, the radius will vary exponentially with the phase of the pumping signal at the instant when the electron enters. At an average for all possible phases an increase in the radius of the electron paths is then obtained. Consequently, the electrons enter the third coupling member with a radius of the helical path increased at the expense of the energy of the pumping signal source, so that an amplified signal is obtained.

The device according to the invention is a variation of the above device. It is characterized in that the electron beam is guided along a curved path over part of its travel between the electron gun and the collector electrode by means of a plurality of coaxial, arcuate deflecting electrodes arranged on either side of the beam.

The path of an electron beam acted upon by electrostatic agency in an electron beam tube, the beam being bent along a curved path through a given angle by two radially spaced apart coaxial arcuate deflection electrodes, arranged one on each side of the electron beam, is known under the name of cycling track. Between the electrodes is applied a voltage difference, the innermost electrode is positive and the outermost is negative. The voltage difference is chosen with a view to the velocity of the incoming electrons and the desired curvature of the path and hence of the electrodes. The fundamental idea is that an electron entering at a given place between the electrodes of the cycling track has to follow a path which is coaxial to the two electrodes. An electron entering slightly at the side of this path of equilibrium between the electrodes of the cycling track is exposed to a force towards the path of equilibrium and performs an oscillating movement around the path of equilibrium. The frequency of this movement is determined by the attractive force of the electric field. The oscillation frequency associated with this direct-current adjustment will be termed hereinafter the natural frequency f,,. Half the wavelength of the oscillation corresponds to 127. This particular property of the cycling track is i.n dependent of its length.

In the device according to the invention the signal voltage applied to the first coupler superimposes an alternating voltage on the aforesaid direct-current adjustment, so that the electrons are set oscillating in transverse direction. If the signal frequency f, is not equal to the natural frequency f it is found that the signal propagation can be described by two transverse waves, which are termed the fast wave and the slow wave. Theoretically it is now possible to choose the shape and the dimensions of the first coupler with respect to the electron velocity so that only the fast wave is produced. In accordance with the ratio between the signal frequency and the natural frequency and in accordance with the signal frequency itself the coupler is constructed in the form of deflection plates or in the fonm of a delay line having a substantially transverse electric field, for example, a folded Lecher line. If the coupler is shaped in the form of deflection plates, these plates may be constituted by two circular curved plates which constitute at the same time part of the cycling track structure. With respect to direct voltage a potential difference prevails between these plates, which is required for the circular path of equilibrium of the electrons; the plates are furthermore connected to the signal source.

The shape, the dimensions and the load of the third coupler are chosen so that it is coupled with the trans verse fast Wave and absorbs, in principle, all signal energy coming 1n.

The amplification is obtained at the expense of the energy supplied by the pumping signal source in the form of an inhomogeneous electric field acting mainly transversely upon the beam and having a frequency equal to twice the natural frequency. This second coupler may be constructed, for example, in the form of four plates, of which two are curved in the form of a circle, constituting part of the cycling track structure and two other plates are orthogonal thereto, each on one side of the electron beam. The opposite plates have the same alternating voltage potential. Moreover, the two plates orthogonal to the circular plates have the same directvoltage potential.

As compared with the known device the device ac cording to the invention has the advantage that no magnetic field need be used. Moreover, the dimensions of the curved tube may be smaller than those of the tube of known structure.

In order to prevent the third coupler from absorbing also the amplified noise of signal frequency, the fast wave components of the noise of signal frequency are to be removed from the electron beam before the latter enters the second coupler. By correct choice of the load impedance of the first coupler it is, in principle, possible to absorb completely the fast wave components of the noise of signal frequency occurring on the beam after the latter has left the gun.

Since the signal frequency i is not equal to the natural frequency f a new signal is produced during the amplification in the second coupler, the frequency 2f f of which signal is the image of the initial frequency i with respect to the frequency f If the beam when entering the second coupler, has a signal of the frequency 212,- S a signal of the frequency f would be produced during amplification. It is therefore important to choose the load impedance of the first coupler not only so that the fast wave components of the noise of the signal frequency i occurring on the beam after it has left the gun, are completely absorbed, but also so that the fast wave components of the noise of the image signal frequency 2f S are completely absorbed. The latter is only possible when the signal frequency f does not differ materially from the natural frequency f and hence from the image signal frequency 2f since the first coupler is designed, in principle, for the signal frequency.

If 2f,, 5 should assume a negative value, this would mean that the image signal frequency is negative. A signal of negative frequency corresponds theoretically with a signal having the same amount of positive frequency, but having a flow of energy of opposite sign. The fast wave of a signal of negative frequency may therefore be considered to be the slow wave of a signal of the same positive frequency. Since it is not possible to absorb a slow wave, it is obvious that in this cas the fast wave of image signal frequency cannot be absorbed without the need for further means. With respect to the amplification, it should be noted that in this case it does not take place only at the expense of the energy supplied by the pumping signal source but also by the conversion of kinetic beam energy into signal energy.

It is also possible to provide between the electron gun and the first coupler an additional coupler, which serves to eliminate the noise of the beam leaving the electron gun. If the signal frequency and the natural frequency do not differ much, the load impedance of this additional coupler may be chosen so that, in principle, the fast wave components of the noise of signal frequency and of image signal frequency are completely absorbed. This has the advantage that the first coupler then serves only to apply the signal to be amplified to the beam. If the signal frequency and the natural frequency differ considerably from each other, the shape and the load impedance of the additional coupler may be chosen so that, in principle, the fast wave components of the noise of image signal frequency are completely absorbed, whilst the load impedance of the first coupler may then be chosen so that, in principle, the fast wave components of the noise of signal frequency are completely absorbed.

If in the case of a great difference between the signal frequency and the natural frequency, the elimination of noise from the beam and the application of the signal to be amplified to the beam are to be carried out separately, two additional couplers are required between the electron gun and the first coupler; one coupler being constructed so that in principle, the fast wave components of the noise of signal frequency and the other so that, in principle, the fast wave components of the noise of image signal frequency are completely absorbed.

The wavelength of the oscillation performed by electrons located outside the path of equilibrium may be reduced. To this end, in accordance with the invention, the electron beam is subjected to a magnetic field orthogonal to the direction of travel of the electrons, the effect of this field on the electrons being opposite that of the electric field operating between th deflection electrodes. As compared with the case in which no magnetic field is available, the electric field between the deflection electrodes is required to be enhanced in the presence of a magnetic field, in order to re-establish the equilibrium. Since the direct-current velocity of the electrons remains th same, the natural frequency f is higher with a reduced wavelength. This arrangement has the advantage that signals of higher frequency can be amplified, whereas nevertheless the difference between the signal frequency and the natural frequency is not high. Although this arrangement requires a magnetic field, it has the advantage over the known device, that this magnetic field is much shorter. The device may be realized by arranging the tube between the pole shoes of a permanent magnet or an electro-magnet.

One embodiment of the device according to the invention will now be described more fully with reference to the drawing.

FIG. 1 shows an electron beam tube for use in a device according to the invention in a sectional view taken on the path of the electrons.

FIG. 2 shows an axial section of the second coupler of the tube shown in FIG. 1 and, moreover, the electrical connections thereof.

FIG. 3 shows an axial section of the first coupler of the tube shown in FIG. 1 and, moreover, the electrical connections thereof.

The device shown in FIG. 1 comprises an electron beam tube having an exhausted envelope 3t), inside of which provision is made of an electron gun 4- to produce an electron beam and a collector 5 for collecting the electron beam, the gun 4 and collector 5 being connected to a DC. supply source 45 in the conventional manner. Both the envelope and the electron gun and the collector electrode may be of known structure.

In the direction from the electron gun 4 towards the collector electrode 5 are arranged along the beam, in order of succession: the first coupler 1, the second coupler 2 and the third coupler 3.

The coupler 1 comprises tWo radially spaced apart coaxial, arcuate conductors 6 and 7 which may be comprised of sections of circular cylindrical surfaces. These conductors are connected to a direct-voltage source 27 so that the conductor 6 is negative with respect to the conductor 7, the mean voltage of the two conductors being equal to the equilibrium voltage to be described hereinafter. The conductors are furthermore connected by way of a capacitative coupling, such as capacitors 24 and 25, to the signal source 26, which supplies the signal to be amplified having the frequency i The coupler 3 is of the same kind and also comprises two radially spaced apart coaxial arcuate conductors 8 and 9, which may be sections of circular cylindrical surfaces. These conductors are connected to the directvoltage source 41 in order to maintain the cycling track. The amplified signal of the frequency i is derived in load 42 from the conductors 8 and 9 via capacitors 43 and 44.

The second coupler 2 comprises four plates, 10, 11, 18 and 19, with plate 19 being behind plate 18 in FIG. 1. Plates 10 and 11 constitute radially spaced apart coaxial, arcuate conductors, which may be sections of circular cylindrical surfaces. Conductors 10 and 11 are gonnected to opposite terminals of direct-voltage source Separate conductors 12 and 13 are arranged alongside the beam between the electron gun 4 and the first coupler 1, which conductors serve as an anode. The conductors 12 and 13 are connected to source 45, the mean voltage of the conductors 12 and 13 being the equilibrium voltage of the device. In order to ensure that the electrons remain in the circular path between the first coupler 1 and the second coupler 2, the conductors 14 and 15, also connected to source 45, are arranged between these two couplers, which conductors serve as postdeflection electrodes, of which the mean voltage is equal to the equilibrium voltage. To the same end the conductors 16 and 17, connected to the source 45, are provided between the second coupler 2 and the third coupler 3. The conductors 13, 15 and 17, as is shown in the drawing, may be connected to each other. This is advantageous in order to avoid parasitic coupling between the couplers.

FIG. 2 is an axial sectional view of the second coupler 2. Numerals and 11 designate radially spaced apart coaxial, arcuate conductors and 18 and 19 denote the two conductors arranged at right angles to the conductors 10 and 11, on opposite sides of the electron beam. The conductors 18 and 19 are connected to each other for direct currents and connected to one output of the alternating-voltage source 20 of the frequency 2f The conductors 10 and 11 are capacitatively coupled via the capacitors 21 and 22 with the other output of the alternating-voltage source 20. The conductors 10 and 11 are furthermore connected to the direct-voltage source 23.

FIG. 3 is an axial sectional view of the first coupler 1. In this case reference numerals 6 and 7 designate the coaxial arcuate conductors. They are coupled capacitatively via the capacitors 24 and 25 with the signal source 26 and furthermore with the direct-voltage source 27. The third coupler 3 is constructed similarly.

In a practical embodiment of the device according to the invention the radius of the arcuate conductors 6 and 8 was 2.05 cms., that of the arcuate conductors 7 and 9, 1.95 cms. that of the arcuate conductor 10, 2.125 cms. and that of the arcuate conductors 11, 1.875 cms. The first coupler and the third coupler extended through an arc of and the second coupler through an arc of 142. In the second coupler the distance between the conductors 10 and 11 was 0.25 cm. and between the conductors 18 and 19, 1 cm.

With the operation without magnetic field, the following adjustment was possible. The mean velocity of the electrons of the path of equilibrium of a radius of 2 crns. was 18.7)(10 m./sec. Herewith was associated a natural frequency f of 10.3 mc./s. The transverse electric field intensity between the arcuate conductors was 0.7 v./mrn.

When a magnetic field was applied at right angles to the direction of travel of the electrons of 537 Gauss, as indicated by the letter H in FIG. 1, the same mean velocity of the electrons in the path of equilibrium was associated with a natural frequency of 1505 mc./s. In order to maintain the cycling track a transverse electric field of 100 v./m.m. was required. The pump ing signal frequency was 3010 mc./s.

What is claimed is:

1. A fast wave electron beam tube comprising an electron gun for producing a beam of electrons, a collector electrode positioned in the path of said beam, and first, second and third couplers coupled to said beam between said electron gun and said collector electrode in that order, at least said, second coupler comprising a pair of radially spaced apart arcuate coaxial conductors positioned on opposite sides of said beam, and means for applying a direct potential between said pair of arcuate conductors whereby said beam is guided along a curved path over at least a part of the distance between said electron gun and collector electrode, a source of input signals, means for applying said input signals to said first coupler to produce an electric field acting transversely upon said beam to obtain a fast wave, a source of pumping signals, means for applying said pumping signals to said second coupler to produce an inhomogeneous electric field acting transversely upon said beam, and output circuit means connected to said third coupler.

2. A fast wave electron beam tube comprising an electron gun for producing an electron beam, a collector electrode positioned in the path of said beam, and a plurality of pairs of arcuate coaxial radially spaced apart conductors positioned along said beam with the conductors of each said pair of conductors being on opposite sides of said beam, said conductors comprising sections of circular cylindrical surfaces, means applying a direct potential between the conductors of each of said pairs of conductors whereby said beam is guided along a curved path and electrons entering said path at the side of the equilibrium point of said path oscillate about said equi librium point, a source of input signals, means applying said input signals to one pair of said conductors to produce an electric field acting transversely upon said beam to obtain a fast wave, a source of pumping signals, means applying said pumping signals to another pair of said conductors between said first pair and said collector electrode to produce an inhomogeneous electric field acting transversely upon said beam, and output circuit means connected to a third pair of said conductors between said other pair and said collector electrode.

3. The arrangement of claim 2 comprising means providing a magnetic field, and means directing said field in a direction orthogonal to the direction of travel of electrons of said beam, said field having a polarity to deflect said electrons of said beam in a direction opposite to the deflection produced by the electric field produced by said conductors.

4. A fast wave electron beam tube comprising an electron gun for producing an electron beam, a collector electrode positioned in the path of said beam, and first, second and third couplers coupled to said beam in that order between said gun and said collector electrode, each of said couplers comprising a pair of arcuate coaxial radially spaced apart conductors, with the conductors of each pair being disposed on opposite sides of said beam, whereby said beam is guided along a curved path, said conductors comprising sections of circular cylindrical surfaces, said second coupler comprising in addition a pair of conducting plates disposed along opposite remaining sides of said beam, said pair of conducting plates being insulated from said conductors of said second coupler.

5. A fast wave amplifier comprising an electron beam tube having an electron gun for producing an electron beam, a collector electrode positioned in the path of said beam, and first, second and third couplers coupled to said beam in that order between said gun and said collector electrode, each of said couplers comprising a pair of arcuate coaxial radially spaced apart conductors, with the conductors of each pair being disposed on opposite sides of said beam, whereby said beam is guided along a curved path, said conductors comprising sections of circular cylindrical surfaces, said second coupler com prising in addition a pair of conducting plates disposed along opposite remaining sides of said beam, said pair of conducting plates being insulated from said conductors of said second coupler, means providing a direct potential between the conductors of each pair of conductors, a source of input signals, means applying said input signals to said first coupler to produce an electric field acting transversely upon said beam to obtain a fast wave, a source of pumping signals, means connecting said source of pumping signals between said conductors of said second coupler and said conducting plates of said second coupler whereby said pumping signals produce an inhomogeneous electric field acting transversely upon said beam, and output circuit means connected to said third coupler.

6. The amplifier of claim 5 comprising means providing a magnetic field directed normal to the direction of said beam, said field having a polarity to deflect electrons of said beam in a direction opposite to the direction 7 they are deflected by direct potentials between the conductors of each pair of conductors.

References Cited by the Examiner UNITED STATES PATENTS 2,464,562 3/ 1949 Dierner 3138O 2,721,954 10/1955 Nygard 313-80 3,178,646 4/ 1965 Ashkin 3304.7

8 OTHER REFERENCES 

1. A FAST WAVE ELECTRON BEAM TUBE COMPRISING AN ELECTRON GUN FOR PRODUCING A BEAM OF ELECTRONS, A COLLECTOR ELECTRODE POSITIONED IN THE PATH OF SAID BEAM, AND FIRST SECOND AND THIRD COUPLERS COUPLED TO SAID BEAM BETWEEN SAID ELECTRON GUN AND SAID COLLECTOR ELECTRODE IN THAT ORDER, AT LEAST SAID SECOND COUPLER COMPRISING A PAIR OF RADIALLY SPACED APART ARCUATE COAXIAL CONDUCTORS POSITIONED ON OPPOSITE SIDES OF SAID BEAM, AND MEANS FOR APPLYING A DIRECT POTENTIAL BETWEEN SAID PAIR OF ARCUATE CONDUCTORS WHEREBY SAID BEAM IS GUIDED ALONG A CURVED 